Pulmonary sequestration is a defect in the formation of the lungs, which consists in the separation from the main organ of a rudimentary section of lung tissue with autonomous blood flow that does not participate in the gas exchange process. Symptoms may be meager; with an exacerbation of infectious inflammation, it includes fever, weakness, shortness of breath, cough with mucopurulent sputum, hemoptysis; with compression of the esophagus and stomach – a violation of the passage of food. The diagnosis is based on the data of radiography and CT of the lungs, bronchography, bronchoscopy, angiopulmonography. In case of disease, treatment is only operative – sequestrectomy, segmentectomy or lobectomy.
Q33.2 Pulmonary sequestration
Sequestration (from Latin “sequestratio” – separation) of the lung is a congenital pathology with partial or complete separation and independent development of a perversely altered part of the lung tissue (independent blood supply, isolation from ordinary bronchopulmonary structures). Pulmonary sequestration is among the rare anomalies of lung development (1-6%), and among chronic nonspecific pulmonary diseases, its frequency in pulmonology is 0.8-2%.
Sequestration of lung tissue is not involved in respiratory function, has a small size and is usually represented by a cyst-like formation (a single bronchogenic cyst or a cluster of small cysts). The sequestration site is not connected to the vessels of the small circulatory circle (pulmonary artery), but has an abnormal blood supply through additional vessels coming from the descending arc of the thoracic or abdominal aorta or its branches (subclavian and splenic arteries). The main venous outflow from the vicious area is realized through the system of the superior vena cava, less often through the pulmonary veins. Sometimes sequestered tissue can communicate with the bronchi of the affected lung.
Causes of pulmonary sequestration
Pulmonary sequestration is a complex defect caused by a combined violation of the formation of various bronchopulmonary structures. The anomaly develops as a result of teratogenic influences in the early intrauterine phase. The source of the development of disease are additional protrusions of the primary intestine, rudiments of the diverticulum of the esophagus, separated from the organizing lungs and then losing contact with the primary intestine and bronchial tree. Sometimes there may be a connection of the vestige of the lung with the esophagus or stomach with the help of a joint (bronchopulmonary malformation).
According to the theory of traction, the development of pathology is facilitated by a violation of the reduction of the branches of the primary aorta with their transformation into abnormal vessels. Through these vascular branches, the rudimentary fragments of the lung are separated from the normal pulmonary bookmark.
Pulmonary sequestration is often combined with other malformations: ELS – with nonimmune fetal dropsy, anasarca, hydrothorax of the newborn; ILS – with congenital adenomatoid malformation of the lung type 2, rhabdomyomatous dysplasia, tracheo- and bronchopesophageal fistulas, funnel-shaped deformation of the chest, open mediastinum, diaphragmatic hernia, kidney hypoplasia, defects of the spine and hip joints.
There are 2 forms of pulmonary sequestration: intra–lobar (intralobar – ILS) and extra-lobar (extralobar – ELS). In intralobar pulmonary sequestration, the cystic site is located among the functioning lung parenchyma within the boundaries of the visceral pleural leaf (most often in the medial-basal segments of the lower lobe of the left lung) and is vascularized by one or more aberrant vessels. ILS can be considered as a congenital cyst with abnormal blood circulation. Sequestered pulmonary cysts have an epithelial lining and liquid or mucous contents, often not primarily associated with the bronchial tree. In a cystic-altered section of pulmonary sequestration, suppuration occurs sooner or later.
In the extralobar form, the pulmonary sequester has a separate pleural leaf and is isolated from the main organ, being a completely ectopic tissue (an additional pulmonary lobe). ALS is more often observed in the left half of the chest (in 48% of cases), in the right (20%), in the anterior (8%) or posterior (6%) mediastinum, subdiaphragmally (18%), in the abdominal cavity (10%), intrapericardially (isolated cases). ELS is provided by blood exclusively through the arteries of the large circulatory circle (thoracic or abdominal aorta). Microscopically, the ALS tissue includes many undeveloped identical bronchioles, acinuses consisting of irregular-shaped alveolar passages and ordinary or dilated alveoli. In a quarter of cases, ALS is diagnosed prenatally, in 2/3 of cases – in the first 3 months of a child’s life.
The incidence of intra-tumor pulmonary sequestration is about 3 times higher than non-tumor, sometimes their simultaneous presence in one patient is possible. ALS is 3-4 times more common in boys than in girls.
According to clinical criteria , there are 3 forms of pulmonary sequestration:
- bronchiectatic (with melting of adjacent lung tissue and the appearance of secondary communication with the bronchial system);
- pseudotumorous (with scant or absent symptoms)
- cystic abscess (with the development of purulent inflammation of the lung)
Symptoms of pulmonary sequestration
The clinical picture of pulmonary sequestration is determined by the localization of sequestration, the presence or absence of its connection with the respiratory tract, the degree of development of hypoplasia of lung tissue and inflammatory changes. Symptoms of intralobar pulmonary sequestration rarely manifest at the stage of neonatal and early childhood, usually developing at an older age with infection, inflammation, suppuration and breakthrough of cystic sequestration.
With suppuration of the cyst and abscess of the vicious lobe of the lung, the disease begins acutely with fever, weakness, sweating, moderate pain, shortness of breath during exercise, unproductive cough, and with a breakthrough of the abscess – with the release of a significant volume of purulent sputum. Sometimes hemoptysis and pulmonary bleeding are possible, pleural complications are frequent. The course of pulmonary sequestration usually becomes chronic with repeated sluggish exacerbations and remissions. With ILS, there may be a clinic of recurrent pneumonia.
Extralobar pulmonary sequestration often proceeds asymptomatically and begins to bother the patient only in adolescence and later. Non-tumor sequestration can provoke compression of the esophagus, stomach and other organs, which can be manifested by shortness of breath, cyanosis, violation of food evacuation. The risk of infection is extremely low.
Pulmonary sequestration can be complicated by pneumomycosis, tuberculosis, profuse pulmonary hemorrhage and massive hemothorax, tumor formation, development of acute heart failure due to volumetric overload of the heart due to arteriovenous bypass surgery in a sequestered cyst.
Early diagnosis of pulmonary sequestration is difficult due to the similarity of its clinical and radiological symptoms with those of other pulmonary pathology. The diagnosis is established based on the totality of the data of the survey radiography and CT of the lungs, bronchography, bronchoscopy, ultrasound of the abdominal cavity, aortography, angiopulmonography.
Radiologically, intralobar pulmonary sequestration (in the absence of connection with the bronchus and inflammation) is defined as shading of irregular shape of varying degrees of intensity with enlightenment in the thickness or as a cavity formation with or without a horizontal fluid level. With exacerbation around the sequester in the lower lobe of the lung, there is a pronounced deformation of the vascular-bronchial pattern, moderate perifocal infiltration of lung tissue. During bronchography, there is deformation and displacement of the bronchi adjacent to the affected segment of the lung. The bronchoscopic picture of pulmonary sequestration communicating with the respiratory tract corresponds to catarrhal-purulent endobronchitis on the side of the affected lung.
Peritoneal ALS is detected on ultrasound as a clearly delimited formation of homogeneous echogenicity with blood supply through branches of large arteries. The diagnosis is finally confirmed by lung MSCT and angiopulmonography with the establishment of the presence, number and topography of abnormal vessels feeding the sequestration area. Radioisotope scanning of the liver and peritoneography help to distinguish right-sided pulmonary sequestration from the pathology of the gastrointestinal tract. Pulmonary sequestration is often detected during surgery for a chronic purulent process in the lung. The differential diagnosis of pulmonary sequestration is carried out with destructive pneumonia, tuberculosis, a cyst or lung abscess, bronchiectasis, a tumor of the thoracic cavity.
Treatment of pulmonary sequestration
In case of pulmonary sequestration, surgical intervention is required – removal of an abnormal section of lung tissue. If asymptomatic intra–lobar pulmonary sequestration is detected, segmentectomy may be performed, but most often removal of the entire affected pulmonary lobe (usually the lower one) is required – lobectomy. The tactic of surgical treatment of the non-tumor form is to remove the sequestered area (sequestrectomy). The presence of abnormal large arterial vessels of atypical localization during pulmonary sequestration makes it important to make a thorough preliminary diagnosis in order to avoid their intraoperative damage and the development of severe life-threatening bleeding.
The prognosis for the intralobar form in the absence of purulent-septic processes is satisfactory, with extralobar pulmonary sequestration of abdominal localization, as a rule, is better than with its intra–thoracic location.
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